Mild traumatic brain injury (TBI) stemming from exposure to high-intensity blasts is one of the most prevalent injuries sustained by Veterans of Operation Enduring Freedom and Operation Iraqi Freedom. Recent research indicates that many of these Veterans can suffer from chronic difficulties processing auditory information in spite of normal hearing thresholds. Some of the most commonly reported problems include difficulty with speech in noisy or distracting environments, problems with long running speech and recalling lists of instructions, and difficulties on the telephone. Currently, little is known regarding how blast exposure affects the physiology of the auditory system to produce such deficits, nor the potential contributions of comorbid cognitive disorders to auditory processing concerns. In the current study, we aim to use electrophysiology in combination with behavioral testing to better understand how blast- exposure and TBI shape the neural encoding and discrimination of sound, and to probe the influence of cognitive factors on auditory processing. The long term goal of our research program is to develop electrophysiological tools which accurately and reliably reflect auditory function and can be used to improve clinical diagnosis and rehabilitation efforts of adult patients with acquired auditory processing disorder. Our overall objective for this CDA-2 research plan, which is the next step toward attainment of our long-term goal, is to systematically evaluate the utility of cortical and cognitive auditory evoked potentials (AEP) measures to reveal chronic physiological changes in auditory processing in Veterans with previous blast-exposure/TBI, and examine the relationship between these objective physiological measures and behavioral measures of hearing ability. Specifically, we will 1) determine how blast exposure and TBI affect neural discrimination of sound across domains including frequency, timing, intensity, and binaural integration at the level of the auditory cortex, 2) the impact of blast exposure/TBI on cognitive modulation of auditory encoding using cognitive AEPs, and 3) Assess the relationship between cortical and cognitive AEP measures and psychometrically based behavioral measures of auditory processing. We hypothesize that blast-exposed Veterans will demonstrate deficits in both cortical encoding of sound characteristics as evidenced by higher thresholds for detecting changes in sound and reduced amplitudes to changes in sound characteristics in blast- exposed/TBI Veterans compared to age- and hearing-matched control participants. We further predict that blast-exposed/TBI Veterans will show decreased cognitive control of sound encoding compared to control participants, and that cortical and cognitive AEP indices will be well correlated with behavioral measures of hearing ability. The outcomes of this research proposal include a better understanding of the bottom-up vs top-down contributions to auditory processing disorders in Veterans with previous blast-exposure and TBI and will serve as a starting point for developing physiological tools to evaluate auditory concerns in this population. These outcomes are expected to have a positive impact because they increase our knowledge of the impact of blast exposure and TBI on auditory function and will provide a significant step forward towards improved clinical care for these patients. This work will be significant because it is expected to have broad translational implications on the diagnosis and management of adult patients suffering from acquired auditory processing disorders.